(a) Field of the Invention
The present invention relates to a zoom lens system, more particularly to a zoom lens system having a high magnification, a compact size and low aberration.
(b) Description of the Related Art
For a lens shutter camera or video camera to be compact, the zoom lens system must be designed to be compact and as short as possible.
The zoom lens system for a lens shutter camera can generally be classified into two types. A first type has two lens groups, whereas a second type has three lens groups. A compact zoom lens system generally uses the second type with three lens groups. However, compact zoom lens systems for cameras with zoom lens systems with a zoom ratio of greater than 2.0 are rather long and therefore difficult to manufacture.
The lenses installed in zoom lens systems are generally spherical lenses, with the number of lenses increasing considerably in lens systems with a high zoom ratio. The total length of the zoom lens system then increases accordingly which makes it difficult to manufacture such zoom lens system in a compact form.
A conventional compact zoom system with two lens groups is described, for example, in Japanese Laid-Open Patent Application No. Hei 2-284109, Japanese Laid-Open Patent Application No. Hei 7-120673, and U.S. Pat. No. 5,381,270 Japanese Laid-Open Patent Application No. Hei 2-284109 and Japanese Laid-Open Patent Application No. Hei 7-120673 describe zoom systems with zoom ratios of 2.0 and as many as eight lenses. Zoom lens systems of this type are difficult to manufacture in compact form. The zoom lens system described in U.S. Pat. No. 5,381,270 also has eight lenses and a zoom ratio of 2.0. Moreover, the total length of the zoom lens system of U.S. Pat. No. 5,381,270 exceeds 30 mm. It is therefore quite difficult to manufacture compact zoom lens systems.